Missing Data (The Effect, Videos on Causality, Ep 68)

[@haraldurkarlsson1147]

As NRC fellow at NASA JSC I studied Martian Meteorites for my postdoc. Some of the samples were onsite while others had to be obtained from natural history museums or individual researchers. Although I was fairly successful in obtaining the stones I desired some refused to send or share samples (for reasons typically not given). What type of missing is that?

[@NickHuntingtonKlein]

If you think the decision to withhold the stones from you is related to the characteristics of the stones, that's MNAR. if the choice to withhold is random, it's MCAR. can't be MAR because you're missing the entire observation instead of just some of the values. Yours is more a case of sample selection than missing data (which usually implies you have some variables for your observations but not other variables)

[@haraldurkarlsson1147]

@@NickHuntingtonKlein Interesting. These samples are typically rare and thus curators or individuals do not want to part with a big sample used for destructive analysis (different from simple loans). The material after the analysis had less or no value for some future work. Another reason is that museum curators (I used to be one) are simply not willing to part with rare samples. Finally, some may simply want to do the work you are proposing themselves.

[@joshen2865]

hi, thanks for your great video! I want to ask if there's missing value when I'm analyzing panel data (unbalanced panel data), and I want to use the fixed effect model, will the model still holds when the panel data is unbalanced?

[@NickHuntingtonKlein]

Fixed effects still works unbalanced in general, but there are some slightly different methods to use, especially for things like calculating degrees of freedom. Look up unbalanced panel data methods.